The present invention relates generally to the monitoring and control of the flow of intake air to air handling equipment, such as ventilating and air conditioning equipment, and pertains, more specifically, to a probe and a method for use in monitoring intake air volume in such air handling systems.
The measurement and control of the volume of fresh air drawn into the intake of air conditioning and ventilating equipment in a building is of utmost importance in maintaining indoor air quality for promoting the health, safety and comfort of occupants of the building. These measurements usually are carried out in connection with the use of probes placed between an outdoor air intake and the air conditioning and ventilating equipment for the purpose of determining the volume of intake air drawn into the system.
Conventional airflow measurement probes are designed to operate in relatively undisturbed, essentially homogeneous airflow usually found in distribution ductwork and generally require long straight runs of ductwork in order to avoid turbulent airflow and establish the desired homogeneous flow profiles necessary for accurate volume measurement. However, typical intakes to air conditioning and ventilating equipment do not provide adequate space for the long straight runs of ductwork required to avoid turbulent airflow. This is true especially in retrofit installations where existing space often is severely limited. In addition, the volume of fresh air drawn into air handling systems will vary over a very wide range; the ratio of maximum volume to minimum volume often rising to as much as eight to one. Such a range in volume requires a probe which can operate accurately over a wide range of airflow volume. Further, intake air velocities purposely are maintained low in order to avoid drawing in rain, snow and debris, such as leaves and paper. Maximum velocities at intakes typically are one-quarter of the velocities found in distribution ductwork, thus rendering the accurate measurement of airflow at an intake much more difficult. Still further, environmental extremes, either at a single site or among a variety of sites where air handling systems are operated, present a challenge to the ability of probes to perform under all conditions, such as extremes in temperature and humidity.
Air brought into air conditioning and ventilating systems rarely is clean and can be expected to be laden with dirt and some debris. Maintenance in the vicinity of the intake to such systems hardly ever is of a preventive nature. Hence, equipment put into service under such conditions must be capable of operating for extended periods without regular maintenance.
The measurement of air volume at the intake of an air handler is complicated further by the presence of high background noise, usually in the form of short bursts and discontinuities in airflow caused by wind and wind gusts blowing against the air intake. At times, the magnitude of such a noise component can be as large as the airflow itself.
Air conditioning and ventilating equipment intake location and configuration can vary considerably, presenting challenges to the design of a probe which can accomodate a wide variety of such locations and configurations.
The present invention provides a probe and a method for use in monitoring intake air volume in air handling systems and which accomplishes such monitoring while avoiding the problems and accommodating the difficulties outlined above. As such, the present invention attains several objects and advantages, some of which are summarized as follows: Provides a probe and a method for monitoring intake air volume in an air handling system, the probe having a construction enabling effective operation when installed where the intake air is traveling in a turbulent stream; enables accurate measurement of airflow volume over a very wide range of airflow volume, and does so in the presence of turbulence in the airflow; allows accurate monitoring of airflow volume at relatively low air velocities; accommodates extremes in air temperature and humidity for accomplishing accurate airflow volume measurements at a wide variety of installation sites, as well as wide variations in conditions encountered at a single site; resists degradation of performance in the presence of dirt and debris for long-term operation with little or no periodic maintenance; is less sensitive to noise, enabling accurate measurements under a variety of wind conditions encountered at an intake to an air handling system; exhibits a very wide range of operation, enabling greater versatility in applying the probe and the method to various locations and configurations at installations encountered in the field; provides a probe of relatively simple and inexpensive construction, capable of installation with ease at conventional sites for exemplary performance of the method over an extended service life.
The above objects and advantages, as well as further objects and advantages, are attained by the present invention which may be described briefly as a probe for use in monitoring intake air volume in an air handling system, wherein intake air travels in a turbulent stream flowing in a direction downstream from an upstream air intake, the probe comprising: a high pressure chamber having a front wall including an external front face for facing upstream in the turbulent stream, transverse to the direction of flow of the turbulent stream, the front face having transverse dimensions establishing an impact area on the front face great enough to substantially disturb the turbulent stream such that upon placement of the front face in the turbulent stream the stream impacts upon the impact area of the front face for effecting a substantial change in direction of the turbulent stream; first pressure sensing holes in the front wall for establishing a first pressure in the high pressure chamber when, the probe is placed in the turbulent stream; a low pressure chamber having a rear wall including an external rear face for facing downstream in the turbulent stream, transverse to the direction of flow of the turbulent stream, when the front face faces upstream; second pressure sensing holes in the rear wall for establishing a second pressure in the low pressure chamber when the probe is placed in the turbulent stream; a seal between the high pressure chamber and the low pressure chamber for enabling the establishment of a higher first pressure in the high pressure chamber as compared to a lower second pressure in the low pressure chamber; a high pressure output for transmitting information pertaining to the first pressure in the high pressure chamber; and a low pressure output for transmitting information pertaining to the second pressure in the low pressure chamber; whereby the difference between the first pressure and the second pressure provides information pertaining to intake air volume.
In addition, the invention includes a method for use in monitoring intake air volume in an air handling system, wherein intake air travels in a turbulent stream flowing in a direction downstream from an upstream air intake, the method comprising the steps of: placing a probe in the turbulent stream, the probe having a high pressure chamber with a front wall including an external front face for facing upstream in the turbulent stream, transverse to the direction of flow of the turbulent stream, the front face having transverse dimensions establishing an impact area on the front face; substantially disturbing the turbulent stream by placement of the front face in the turbulent stream so that the stream impacts upon the impact area of the front face to effect a substantial change in direction of the turbulent stream; establishing a first pressure in the high pressure chamber indicative of a pressure at the front face when the probe is placed in the turbulent stream; the probe including a low pressure chamber having a rear wall with an external rear face for facing downstream in the turbulent stream, transverse to the direction of flow of the turbulent stream, when the front face faces upstream; establishing a second pressure in the low pressure chamber indicative of a pressure at the rear face when the probe is placed in the turbulent stream; establishing a higher first pressure in the high pressure chamber as compared to a lower second pressure in the low pressure chamber; transmitting information pertaining to the first pressure in the high pressure chamber; transmitting information pertaining to the second pressure in the low pressure chamber; and utilizing a difference between the first pressure and the second pressure to provide information pertaining to intake air volume.